Application Class in Kotlin #android #application #singleton #class

Application.kt

import android.app.Activity
import android.app.Application
import android.content.Context
import android.content.SharedPreferences
import android.os.Bundle
import android.preference.PreferenceManager
import android.util.Log

class Application : Application(), Application.ActivityLifecycleCallbacks {

    companion object {
        private var instance: Application? = null
        private var sharedPreferences: SharedPreferences? = null
        private var isActive: Boolean = false

        fun applicationContext(): Context {
            return instance!!.applicationContext
        }

        fun getSharedPreference(): SharedPreferences? {
            return sharedPreferences
        }

        fun isActivityVisible(): Boolean {
            return isActive
        }
    }

    override fun onCreate() {
        super.onCreate()
        // initialize for any

        // Use ApplicationContext.
        // example: SharedPreferences etc...
        instance = this
        val context: Context = Application.applicationContext()
        registerActivityLifecycleCallbacks(this)
        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(applicationContext)
    }

    override fun onActivityPaused(activity: Activity?) {
        isActive = false
    }

    override fun onActivityResumed(activity: Activity?) {
        isActive = true
    }

    override fun onActivityStarted(activity: Activity?) {
    }

    override fun onActivityDestroyed(activity: Activity?) {
    }

    override fun onActivitySaveInstanceState(activity: Activity?, outState: Bundle?) {

    }

    override fun onActivityStopped(activity: Activity?) {
    }

    override fun onActivityCreated(activity: Activity?, savedInstanceState: Bundle?) {
    }


}